High resolution, multispectral, wide field of view retinal imager

ABSTRACT

An ophthalmic instrument (for obtaining high resolution, wide field of area multi-spectral retinal images) including a fundus retinal imager, (which includes optics for illuminating and imaging the retina of the eye); apparatus for generating a reference beam coupled to the fundus optics to form a reference area on the retina; a wavefront sensor optically coupled to the fundus optics for measuring the wavefront produced by optical aberrations within the eye and the imager optics; wavefront compensation optics coupled to the fundus optics for correcting large, low order aberrations in the wavefront; a high resolution detector optically coupled to the imager optics and the wavefront compensation optics; and a computer (which is connected to the wavefront sensor, the wavefront compensation optics, and the high resolution camera) including an algorithm for correcting, small, high order aberrations on the wavefront and residual low order aberrations.

FIELD OF THE INVENTION

The present invention is directed to an improved fundus retinal imagingsystem which provides high resolution multispectral retinal images overa wide field of view to permit early diagnosis of various pathologiessuch as diabetic retinopathy, ARMD (age related malocular degeneration)and glaucoma. More specifically, the present invention relates to aconventional fundus retinal imager combined with, inter alia, amultispectral source, a dithered reference, a wavefront sensor, adeformable mirror, a high resolution camera and deconvoluting softwareto produce wide field, high resolution, multispectral images of theretina.

BACKGROUND OF THE INVENTION

The ability to resolve fine details on retinal images can play a keyrole in the early diagnosis of vision loss. Certain biochemical andcellular-scale features, which may be present in the early stages ofmany retinal diseases (e.g., ARMD), cannot be detected today withcurrent funduscopic instruments because of the losses in spatialresolution introduced by the ocular medium of the eye and the lack ofselectable spectral data. Additionally, the presence of aberrationswithin the eye limits the effective input pupil size of a standardfundus retinal imager to about 2 mm. This limit leads to a decrease inthe contrast of the small image details due to diffraction effects.

A partial solution to the foregoing problems is to use an adaptiveoptical system, first for measuring aberrations and then for correctingsuch aberrations. With such a system, it is possible to increase thesystem pupil diameter up to 7-8 mm and achieve a resolution on the orderof 10 μm. The feasibility of this approach has been demonstratedrecently by J. Liang et al., “Supernormal vision and high-resolutionretinal imaging, through adaptive optics,” J. Opt. Soc. Am. A/Vol. 14,No. 11/November, 1997. They report constructing a fundus retinal imagerequipped with adaptive optics that permits the imaging of microscopicstructures in living human retinas. The optical system, which isillustrated in FIG. 2 of this reference, includes a deformable mirrorfor wavefront compensation and a wavefront sensing module including aHartmann-Shack (also known as a Shack-Hartmann; hereinafter abbreviated“S-H”) wavefront sensor. Collectively, the S-H sensor, (which is used tomeasure the eye's optical aberrations) and the deformable mirror (whichis used to make small corrections of the optical aberrations) issometimes referred to as an adaptive optics system. The deformablemirror is positioned in a plane which is conjugate with both the eye'spupil plane and the front surface of the lenslet array of the S-Hwavefront sensor. The S-H wavefront sensor is described in detail in J.Liang, et al., “Objective measurement of wave aberrations of the humaneye with the use of a Hartman-Shack wave-front sensor,” J. Opt. Soc.Am./Vol. 11, No. 7/July 1994. The displacement of the image, of each ofthe lenslets in the S-H wave front sensor, on a CCD gives informationrequired to estimate the local wavefront slope. From the array ofslopes, the wavefront is reconstructed via a least squares techniqueinto Zernike modes. In operation, a point source produced on the retinaby a laser beam is reflected from the retina and received by the lensletarray of the S-H wavefront sensor such that each of the lenslets formsan image of the retinal point source in the focal plane the CCD detectorlocated adjacent to the lenslet array. The output signal from the CCDdetector is acquired by a computer, which processes the signal andproduces correction signals which, via a feedback loop, are used tocontrol the deformable mirror.

There are a number of limitations associated with the above describedinstrumentation including:

1. Sensitively to speckle modulation within the eye;

2. The deformable mirror can only provide limited correction;

3. It is a panchromatic instrument, not multispectral;

4. It operates with a limited field of view, on the order of 2-5degrees; and

5. Several renditions of the S-H output are required to estimate thewavefront.

Further, while it is claimed that it is useful in determiningaberrations beyond defocus and astigmatism and providing improvedimaging inside of the eye, there is no discussion of its use as aclinical instrument to be used in the diagnosis of the major causes ofvision loss and blindness. Finally, the Liang et al. instrument is alaboratory device composed of very expensive one-of-a-kind components.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide, in association withany commercially available fundus imager, an improved, low bandwidthadaptive optics system and an optimized depth sensitive deconvolutiontechnique to increase retinal imaging resolution and field of view, tothereby enable a clinical device to improve the level of opthmologicalhealthcare.

It is another object of the present invention to provide a deconvolutiontechnique which takes into account the reflectance of difficult colorsfrom the various layers of the retina to provide a high spatialresolution, multi-spectral image over a wide field of view.

It is another object of the present invention to provide a fundus basedopthalmic instrument which has resolution at the micron level (i.e.,less than the size of a cell).

It is yet another object of the present invention to provide a retinalimaging system which uses a scanning (or dithered) reference spot tomitigate the speckle problems associated with the instrumentationdisclosed by Liang et al. and which allows wavefront estimates andimages of the retina to be taken with one exposure instead of multipleexposures.

It is yet another object of the present invention to correct for large,low order aberrations (e.g., tip, tilt, focus, and astigmatism) using abimorph adaptive optical element.

It is yet still another object of the present invention to use postimage depth sensitive deconvolution techniques to correct for high orderaberrations (e.g., coma, trifocal, spherical, and higher terms) andremove residual low order aberrations.

It is yet a further object of the present invention to provide theforegoing in an affordable attachment to existing fundus retinalimagers.

The foregoing and other objects will be apparent from the disclosurewhich follows.

SUMMARY OF THE INVENTION

An ophthalmic instrument having a wide field of view (up to 20 degrees)including a retinal imager, (which includes optics for illuminating andimaging the retina of the eye); apparatus for generating a referencebeam coupled to the imager optics to form a reference area on theretina; a wavefront sensor optically coupled to the imager optics formeasuring the wavefront produced by optical aberrations within the eyeand the imager optics; wavefront compensation optics coupled to theimager optics for correcting large, low order aberrations in thewavefront; a high resolution detector optically coupled to the imageroptics and the wavefront compensation optics; and a computer (which isconnected to the wavefront sensor, the wavefront compensation optics,and the high resolution camera) including an algorithm for correcting,small, high order aberrations on the wavefront and residual low orderaberrations. The wavefront sensor includes a Shack-Hartmann wavefrontsensor having a lenslet array and a detector positioned in the frontsurface of the lenslet array for producing a Hartmannogram. The computerincludes means for estimating the wavefront from the Hartmannogram andsending a correction signal to the wavefront compensation optics tocorrect large, low order aberrations in the wavefront. Only oneHartmannogram is required, thereby reducing the exposure of the retinato the spot, and avoiding the need to register successiveHartmannograms. The wavefront compensation optics includes a deformablemirror, such as a bimoph mirror. The algorithm for correcting small,high order aberrations includes a deconvolution algorithm which utilizesinformation from both the wavefront sensor and the high resolutiondetector. The deconvolution algorithm includes an algorithm forestimating the wavefront sensed by the wavefront sensor, means forestimating the Optical Transfer Function of the wavefront, and WeinerFilter Estimation means. The deconvolution algorithm also includes imagereconstruction algorithms. The instrument also includes a plurality offilters and the deconvolution algorithm also accounts for thereflectance of various wavelengths of light from different depths withinthe retina to produce a multispectral deconvoluted image of the retina.The instrument also includes a mechanism for dithering the referencebeam, including a rotatable wedge. Because the instrument produces awide field of view, a large format, high resolution detector isrequired. The instrument, less the retinal imager, is an adaptive opticssystem which can be used in association with a number of commercialimagers, including fundus imagers.

A method of obtaining high resolution, wide field of view, multispectralimages of the retina from the apparatus of the present invention.

These and other objects will be evident from the description thatfollows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial block diagram/partial optical schematic of thepresent invention, including a fundus imager;

FIG. 2 is a side elevation showing a conventional fundus retinal imagerin association with, for instance, the housings for the improvedadaptive optics and high resolution camera of the present invention;

FIG. 3 is a schematic diagram illustrating the principal softwarecontrols and data flow of the present invention;

FIG. 4A is an illustration of the intensity distribution within a pupilplane of the eye produced by an unscanned reference beam;

FIG. 4B is the corresponding Hartmannogram produced by an unscannedreference beam;

FIG. 5A illustrates the intensity distribution within a pupil plane ofthe eye produced by the dithered reference beam of the presentinvention;

FIG. 5B is the corresponding Hartmannogram produced by the ditheredreference beam of the present invention;

FIG. 6A shows the layers of the retina where various wavelengths oflight are reflected;

FIG. 6B is a graph showing the OTF (Optical Transfer Function) of theeye vs. Spatial Frequency for light in the range of, respectively, 650nm, 560 nm and 450 nm;

FIG. 7 is a sample view from one of the monitors incorporated in thepreferred embodiment of the present invention, showing the Hartmannogramand a setting used to operate the wavefront sensor;

FIG. 8 is a view of a sample screen from the other of the monitorsincorporated in the preferred embodiment of the present invention,showing the type of imagery used to align the fundus retinal imager andthe imagery obtained from the high resolution detector;

FIG. 9 is a flow diagram illustrating the algorithms used for thedeconvolution and the image reconstruction of the present invention;

FIG. 10 is a flow diagram illustrating the application of thecolor-depth sensitive deconvolution algorithms for three wavelengths oflight to produce color, depth sensitive deconvolution; and

FIG. 11 is a table comparing the features achieved by the presentinvention with the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 1, improved retinal imaging system 11 includesfundus retinal imager 13, light source 15, filter assembly 17, ditheredreference source generator 19, wavefront sensor 21, deformable mirrorassembly 23, large format, high resolution detector 25, computer 27 andmonitors 29 and 31.

In the present embodiment, fundus retinal imager 13 is a JST ZOMZ, ModelKFG3 which provides collimated output 14 . However, as those skilled inthe art will appreciate other fundus imagers such as the Zeiss FF4 orFF5, the Topcon TRC-50 series or the Canon CF-60 series or CR5-45 canalso be used. Light source 15 and filter assembly 17 are connected tofundus retinal imager 13 via fiber optic cable 33 and the standard fiberoptic port 35 provided on fundus retinal imager 13. Source 15 includesan illumination lamp such as a tungston, xenon or metal halide lamp (notshown). Filter assembly 17, which is controlled by computer 27 viacontrol line is, includes up to 10 filters for use in creatingmultispectral images. Fundus retinal imager 13 includes UV and IRblocking filters (not shown). Filter assembly 17 also includes (a)mechanism(s) (not shown) for selectively positioning a particular filterin the optical path between source 17 and fiber optic cable 33.

Dithered reference source generator 19 (which is controlled by computer27 by a control line (not shown)) includes a source 41 of collimatedlaser light having, for example, a wavelength of 670 nm (to form areference spot on the back of the retina) and a rotating wedge 43 forscanning (or dithering) the beam 45 from source 41. Wedge 43 is amirrored wedge whose wedge angle is used to set the desired ditheredspot area. The speed of rotation, which is adjustable, is determined bythe exposure time of wavefront sensor 21 and the power of source 41.Collimated beam 45 is first reflected by beam splitter 47 and then bymirror 46 to wedge 43. Beam 45 is then optically connected to theoptical system (not shown) of fundus retinal imager 13 via mirror 48,beam expanding optics 50, and beam splitters 49 and 63. The internaloptical system of fundus retinal imager 13 (not shown) focuses beam 45into the back surface of the retina of the eye being examined.

Wavefront sensor 21 includes a S-H lenslet array 51 and a CCD detector53, the image plane of which is positioned in the focal plane of array51. Wavefront sensor 21 is connected to computer 27 via control and datacable 5 5. Detector 53 is a commercially available low noise sensor(e.g. a Hitachi KP-F2A).

The image plane of high-resolution detector 25 is placed in the imageplane 61 of fundus retinal imager 13. The two are optically coupled bybeam splitters 63 and 49, mirrored, deformable surface 65 of adaptiveoptics mirror 67, and imaging lens 69. Adaptive optics mirror 67 iselectrically connected to wavefront sensor electronic drivers 71 viapower cable 72 and control cable 73. In turn, electronic drivers 71 isconnected to computer 27 via cable 75. Deformable mirror assembly 23,including adaptive optics mirror 67 (which is a bimorph mirror) isdescribed in A. Kudryashov et al., “Bimorph Mirrors for Correction andFormation of Laser Beams,” Proceedings of the 2^(nd) nd InternationalWorkshop on Adaptive Optics for Industry and Medicine, World Scientific,pp.193-199. Preferably, detector 25 is a full-frame, large format CCDimage sensor such as the Electron CFK-3020 incorporating an FTF 3020-M(Phillips) detector having 3072(H)×2048(V) active pixels. The largeformat is necessary because the field of view produced by the wavefrontsensor 21, adaptive optics 23, and fundus retinal imager 13 are capableof providing up to 20 degrees.

With reference to FIG. 2, fundus retinal imager 13 includes a base 81,joystick control 83 for aligning the optics (not shown) with the eye ofa patient. Fundus retinal imager 13 also includes a chin rest 85 and aforehead rest 87. The adaptive optics of the present invention (i.e.,wavefront sensor 21 and deformable mirror assembly 23) and highresolution detector 25 are supported in housing 89.

The overall operation of the hardware and software of retinal imagingsystem 11, is best described with reference to FIG. 3. Main program 91operates a number of subroutines and hardware to control the variousfunctions of the system including frame grabing, the storage (bothtemporarily and permanently) of data, and the processing of imagery.Data interface 93, which is turned on and run by main program 91, isused to supply live images of the retina to monitor 29 from CCD detector95 (e.g. a JAI CV-M50 IR), which is running continuously, and which ispart of fundus retinal imager 13). Detector 95 is connected to computer27 by data and control cable 97. Computer 27 is connected to monitor 29via data cable 99. Subroutine 101 runs the balance of the fundusimager's electronics (e.g. illumination controls, target fixationcontrols). Subroutine 103, which is controlled by program 91, includes aconventional algorithm for wavefront estimation based on the centroidscontained in the Hartmannogram, and a conventional algorithm forconverting the physical description of the wavefront to the commandsused to control adaptive optics mirror 67 (to alter the slope ofdeformable surface 65) and estimating the Optical Transfer Function usedin the deconvolution calculations discussed below. Detector 53, which isalso continuously running, sends Hartmannograms to computer 27 via dataand control lines 55 and 104. Subroutine 103 also controls datainterface 105, sends wavefront data to memory 107 (for temporarystorage) and wavefront data to hard drive 109 (for permanent storage).Main program 91 also sends data, via control and data line 75/111, toelectronic drivers 71 for changing the contour of deformable surface 65using data from memory 107. Finally, program 91 controls high resolutionimage subroutine 113 which, in turn, controls data interface 115 (orequivalent), which grabs images off high resolution CCD detector 25 viacontrol and data cable 117. Image data is transferred from detectorinterface 115 to subroutine 113 which, after processing as explainedbelow, is transferred to memory 107. While the foregoing has referenceddata interfaces 93, 105 and 115, those skilled in the art willappreciate that alternate hardware/software combinations, such as aframe graber, can be used to capture the respective images fromdetectors 25, 53 and 91.

A major problem with the prior art has been the speckle-like reflectionof the laser light reference beam from the retina. Without dithering theresulting image of the pupil plane on detector 53 of wavefront sensor 21is highly scintillated. FIG. 4A illustrates the speckle-like patternthat the human eye creates. FIG. 4B illustrates the correspondingHartmannogram. As is apparent from this latter figure, the shape of thespots on the Hartmannogram is highly irregular. This, in turn, makesdetermination of the centroids of the spot's centers difficult which, inturn, greatly reduces the accuracy of the wavefront estimation.

To overcome this problem retinal imaging system 11 incorporates a noveldithered reference source generator 19, which scans reference beam 45over a small patch of the retina. In the present embodiment the scanningpatch is 200-300 μm in diameter. Wedge 43 has a scanning speed of 50-100Hz. The results achieved are illustrated in FIG. 5A, which is an imageof the same human eye used in the generation of the image illustrated inFIG. 4A, but taken with mirrored wedge 43 operating. With the foregoingscanning rate, during the integration time of CCD detector 53 (i.e., 30ms), the speckle pattern is much improved. Consequently, the intensitymodulation within the pupil plane of the wavefront sensor becomes muchsmaller. The spots on the resulting Hartmannogram, illustrated in FIG.5B, became more regular (e.g., Gaussian like). This results in anincrease in the accuracy of the wavefront estimation of, approximately,20 times that achieved by the prior art. Additionally, the timenecessary to correct the aberrations in the eye is considerably reduced,resulting in less exposure of the retina to the laser reference beam.And, because with instrument 11 only one Hartmannogram is necessary, asopposed to the multiple Hartmannograms required by the prior artadaptive optics, the necessity of registering a series of successiveHartmannogram images (which requires a considerable amount of processingtime) and the inaccuracies inherent in such registering is avoided.(Registration is necessary with the prior art because the eye shiftsslightly between successive images due to sacades, an involuntary motionof the eye.

In operation, after the patient's eye has been dilated, the patient'shead is properly positioned by chin rest 85 and brow rest 87 so that thepatient's eye is properly aligned with the optical axis (not shown) offundus retinal imager 13. This is determined by viewing the live, realtime, video data from CCD 95 on monitor 29. Once proper alignment isachieved, laser 41 is energized through use of a shutter (not shown), sothat dithered reference beam 45 is placed on the retina of the eye beingexamined. Through the use of, inter alia, controls 101, the existinginternal optics of the fundus retinal imager 13 are used to focus thedithered reference beam on the retina. The use of a long wavelengthvisible band laser (e.g., 670 nm) places the focus at the back of theretina, as illustrated in FIG. 6A. The reference beam is reflected offthe back of the retina and is reflected by beam splitters 49 and 47 tolenslet array 51 of S-H sensor 21. The resulting Hartmannogram isrecorded by CCD detector 53 and transferred to data interface 105 bycable 55. The image data is then transferred to and processed bysubroutine 103, where the wavefront is estimated, including calculationof the optical transfer function (OTF). As is illustrated in FIG. 3,image data is transmitted to both memory 107 (for temporary storage) andhard drive 109 (for permanent storage). In turn, data is transmittedfrom memory 107 to electronic drivers 71, via control and data line 111,to modify the curvature of surface 65 of bimorph mirror 67, to apply aconjugate wavefront to the image of the retina relayed from fundusretinal imager 13 to high resolution CCD detector 25 (as explained infurther detail below). Via main program 91, data interface 105, dataline 106, and data line 108 the Hartmannogram may be viewed on thescreen of monitor 31, as illustrated in FIG. 7. Operating parameters forwavefront sensor 21 and data interface 105 are also displayed on monitor31.

To capture an image of the retina being examined, the retina isilluminated with white or filtered light (from source 15 via filterassembly 17 and fiber optics cable 33), via internal fundus retinalimager optics (not shown). Such illumination is reflected off thevarious layers of the retina, as illustrated in FIG. 6A, through beamsplitter 49 (which has wavelength sensitive coatings to reflect beam 45and to pass all of the light from source 15) and onto the surface ofbeam splitter 63. The wavefront from the retina is then directed todeformable surface 65 (where the conjugate wavefront is applied tocorrect for low order aberrations), reflected back through beam splitter63, through imaging lens 69 and focused onto focal plane 61 (which isalso the image plane of high resolution detector 25). Image data fromdetector 25 is transferred to computer 27 via data line 117 and datainterface 115 which, in this case, includes an IEEE 1394 driver. Imagedata is transferred to memory 107 via subroutine 113, (which reformatsthe data, adds headers, and synchronizes the simultaneous collection ofthe Hartmannogram and high resolution detector data). Image data is alsosent to monitor 29, via high resolution image processor 119 and dataline 99, for screen display. As illustrated in FIG. 8 an acquisitionwindow displays the most recent high-resolution image 121 from detector25. This can be displayed along with the alignment window live videoimage 123 from detector 95. Main program software can also provide aseries of previously taken high resolution images 125 of the retina.

The deconvolution of the high-resolution images, via high resolutionimage processor 119, from detector 25 and the multispectral applicationof this technique is illustrated in FIGS. 9 and 10. Adaptive opticsmirror 67 is very good at correcting low order aberrations. However, forhigher order aberrations it is less effective. See Table 2 of A.Kudryashov et al., “Bimorph Mirrors for Correction and Formation ofLaser Beams,” where the RMS error for cornea and spherical aberrationsis considerably higher than that for either defocus or astigmatism. Tocorrect for higher order aberrations a deconvolution algorithm is used.See J. Primot et al., “Deconvolution from wave aberrations of the humaneye using a Hartmann Shack wavefront sensor”, JOAS A 7 1598-1608, 1990.The retinal image deconvolution of the present invention to correct forhigher order aberrations is based on the simultaneous acquisition of twoimages of the human eye. One is the high-resolution retinal image 121taken by high resolution CCD detector 25, partially corrected by bimorphmirror 67 (as explained above). The second image is the Hartmannogramfrom lenslet array 51. As discussed above, laser 41 (which is, forexample, a low power semi-conductor laser) is used as the referencesource for the Hartmannogram. Dithered reference source 19 forms asmall, diffraction limited spot on the back of the retina, which sportserves as the reference point source for the wavefront measurements.Subroutine 103 reconstructs the information about wavefront distortionsbased on the analysis of the Hartmannogram. This information about thewavefront is presented as a set of Zernike aberration coefficients (36in this application). From the wavefront shape the Optical TransferFunction (OTF), H(ω), of the eye is calculated. With further referenceto FIG. 9, the high-resolution image from CCD detector 25 is expressedas a function of its intensity distribution, I(r). F(I(r)) is thespatial Fourier transformation of I(r), G(ω) is the Fourier spectrum ofthe high resolution image, and r and ω are the transversal coordinatesin the spatial and frequency domains. From the OTF, H(ω), G(ω) and thesignal-to-noise estimation ψ, a Weiner Filter Estimation is performed onthe retinal image to correct for the high order aberrations (in aniterative process) and, thus, restore small image details of the retina.In this estimation ψ(ω) is the spectral power of the noise, and Y(ω) isthe Wiener Filter Function.

The retina is a complex structure. From the optical point of view it ismanifested in different effective reflection depths, depending on thewavelength. FIG. 6A illustrates these layers of the retina and fromwhich layers various wavelengths of light are reflected. The wavelengthof the reference source is taken into account in the calculation of theOTF. In addition to the deconvolution of the high resolution images andimage reconstruction (as discussed above), the present invention is ableto obtain multispectral images of the retina. This is achieved throughthe use of filters 17, the selection of which is controlled by computer27, via control line 18, and the decomposition of the polychromatic OTFinto three monochromatic OTFs for pre-selected wavelengths representingthe primary RGB colors, as illustrated in FIG. 10. The monochromaticOTFs are determined by high resolution image processor 119 from thewavefront estimation discussed above, and data related to the retinallayers (i.e., depth and wavelength). Then, for each of the monochromaticOTFs, the correcting factor is calculated depending on the wavelengthand effective depth of reflection. Deconvolution for each of the colorchannels of retinal image is carried out using corresponding OTF G(ω)and a Weiner Filter Estimation. Finally a full RGB image is assembled bysuperimposing each of the separately corrected images. FIG. 6Aillustrates the layers of retina, and FIG. 6B the additionalcorresponding OTFs. Calculating the OTFs based on the use of theinformation on the human eye structure (information on depth of theretina layers depending on the reflected light wave-lengths) permitsrestoring of colored retinal images without any additional opticalmeasurements. The depth sensitive deconvolution, DSD, algorithm asdescribed in “Depth sensitive adaptive deconvolution of retinal Images”,A.Larichev, N.Irochnikov and A.Kudryashov, 158-169, EBiOS200 Conferenceon Controlling Tissue Optical Properties, SPIE Proceedings 4162, Jul.5-6, 2000, Technical Program, p.10, consists of three parallel-appliedprocesses, each of them is analogous to the one described above. (SeeFIG. 14) All three share the information on wave-front aberrations,which in combination with the retina layer data permits carrying outdeconvolution for every color subsets of the input picture data. Thenthree monochrome pictures combine in color one, which has much higherquality than the picture, obtained by the conventional algorithms.

FIG. 11 is a table comparing the features of achieved by the presentinvention by the present invention with the prior art. In all cases thefeatures of instrument 11 represent an improvement.

Whereas the drawings and accompanying description have shown anddescribed the preferred embodiment of the present invention, it shouldbe apparent to those skilled in the art that various changes may be madein the form of the invention without affecting the scope thereof.

What we claim is:
 1. An ophthalmic instrument comprising: (a) a retinalimager, said imager including optics for illuminating and imaging theretina of the eye; (b) means for generating a reference beam, saidgenerating means being optically coupled to said imager optics to form areference spot on said retina; (c) a wavefront sensor optically coupledto said imager optics for measuring the wavefront produced by opticalaberrations within said eye and said imager optics; (d) first wavefrontcompensation means optically coupled to said imager optics forcorrecting large, low order aberrations in said wavefront; (e) a highresolution detector optically coupled to said imager optics and saidfirst wavefront compensation means; and (f) computer means, saidcomputer means connected to (i) said wavefront sensor, (ii) said firstwavefront compensation means, and (iii) said high resolution camera,said computer means including second wavefront compensation means forcorrecting, small, high order aberrations.
 2. The instrument of claim 1,wherein said wavefront sensor includes a Shack-Hartmann wavefront sensorhaving a lenslet array and a detector positioned in the front surface ofsaid lenslet array, in operation said wavefront sensor producing aHartmannogram which is transmitted to said computer means.
 3. Theinstrument of claim 2, wherein said computer includes means forestimating said wavefront from said Hartmannogram and sending acorrection signal to said first wavefront compensation means to correctlarge, low order aberrations in said wavefront.
 4. The instrument ofclaim 3, wherein said means for estimating said wavefront requires onlyone said Hartmannogram, thereby reducing the exposure of said retina tosaid spot, and avoiding the need to register successive Hartmannograms.5. The instrument of claim 1, wherein said first wavefront compensationmeans includes a deformable mirror.
 6. The instrument of claim 5,wherein said deformable mirror is a bimoph mirror.
 7. The instrument ofclaim 1, wherein said second wavefront compensation means includesdeconvolution algorithm means, said deconvolution algorithm meansutilizing information from both said wavefront sensor and said highresolution detector.
 8. The instrument of claim 7, wherein saiddeconvolution algorithm means includes means to correct residual loworder aberrations not corrected by said first wavefront compesationmeans.
 9. The instrument of claim 7, wherein said computer meansincludes means for acquiring images from said high resolution detector.10. The instrument of claim 9, wherein said wavefront sensor includesmeans for producing Hartmannograms which are transmitted to saidcomputer means.
 11. The instrument of claim 10, wherein saiddeconvolution algorithm means includes means for estimating thewavefront sensed by said wavefront sensor, means for estimating theOptical Transfer Function of said wavefront, and Weiner FilterEstimation means.
 12. The instrument of claim 11, wherein saiddeconvolution algorithm means includes image reconstruction algorithmmeans.
 13. The instrument of claim 12, wherein said retinal imagerincludes a source for illuminating said retina.
 14. The instrument ofclaim 13, further including a plurality of optical filters and means forselectively positioning any one of said filters between said source andsaid imager optics, whereby said retina may be illuminated by light of apreselected wavelength.
 15. The instrument of claim 14, wherein saiddeconvolution algorithm includes means for accounting for thereflectance of various wavelengths of light from different depths withinsaid retina to produce a multispectral deconvoluted image of saidretina.
 16. The instrument of claim 1, further including a means fordithering said reference beam.
 17. The instrument of claim 16, whereinsaid means for generating a reference beam as a laser.
 18. Theinstrument of claim 16, wherein said means for dithering is a rotatablewedge.
 19. The instrument of claim 1, further includes means forproducing a wide field of view.
 20. The instrument of claim 19, whereinsaid means for producing a wide field of view has a field of view of, upto, 20 degrees.
 21. The instrument of claim 19, wherein said highresolution detector is a large format, high resolution detector.
 22. Theinstrument of claim 1, wherein said retinal imager is a fundus imager.23. An ophthalmic instrument comprising: (a) a retinal imager, saidimager including optics of illuminating and imaging the retina of theeye; (b) means for generating a reference beam for placing a referencearea on said retina; (c) a wavefront sensor coupled to said imageroptics for measuring the wavefront generated by the optical aberrationswithin said eye and said imager optics; (d) wavefront compensation meanscoupled to said imager optics for correcting aberrations; and (e) meansfor dithering said reference beam.
 24. An ophthalmic instrumentcomprising: (a) a retinal imager, said retinal imager including opticsfor illuminating and imaging the retina of the eye; (b) means forgenerating a reference beam, said generating means being opticallycoupled to said imager optics to form a reference area on said retina;(c) a wavefront sensor coupled to said imager optics for measuring theoptical aberrations within said eye and said imager optics; (d) a highresolution detector optically coupled to said imager optics and saidfirst wavefront compensation means; and (e) computer means, saidcomputer means connected to (i) said wavefront sensor, (ii) said firstwavefront compensation means, and (iii) said high resolution camera,said computer means including wavefront compensation means.
 25. Theinstrument of claim 24, wherein said wavefront compensation meansincludes deconvolution algorithm means, said deconvolution algorithmmeans utilizing information from both said wavefront sensor and saidhigh resolution detector.
 26. The instrument of claim 25, wherein saidcomputer means includes means for acquiring images from said highresolution detector.
 27. The instrument of claim 26, wherein saidwavefront sensor includes means for producing Hartmannograms which aretransmitted to said computer means.
 28. The instrument of claim 27,wherein said deconvolution algorithm means includes means for estimatingthe wavefront sensed by said wavefront sensor, means for estimating theOptical Transfer Function of said wavefront, Weiner Filter Estimationmeans, and image reconstruction algorithm means.
 29. The instrument ofclaim 28, wherein said retinal imager includes a source for illuminatingsaid retina.
 30. The instrument of claim 29, further including aplurality of optical filters and means for selectively positioning anyone of said filters between said source and said imager optics, wherebysaid retina may be illuminated by light of a preselected wavelength. 31.The instrument of claim 30, wherein said deconvolution algorithmincludes means for accounting for the reflectance of various wavelengthsof light from different depths within said retina to produce amultispectral deconvoluted image of said retina.
 32. An adaptive opticsdevice for use in association with a fundus retinal imager, said fundusimager including optics for illuminating and imaging the retina of theeye, said device comprising: (a) a wavefront sensor optically coupleableto said fundus retinal imager optics, for measuring the wavefrontproduced by optical aberrations within said eye and said fundus retinalimager optics; (b) first wavefront compensation means, opticallycoupleable to said fundus optics, for correcting large, low orderaberrations in said wavefront; (c) a high resolution detector opticallycoupleable to said fundus optics; and (d) and said first wavefrontcompensation means; and (e) computer means, said computer meansconnected to (i) said wavefront sensor, (ii) said first wavefrontcompensation means, and (iii) said high resolution camera, said computermeans including second wavefront compensation means for correctingsmall, high order aberrations.